The present invention relates to a cationic paint composition. More specifically, it relates to a cationic electrodeposition paint composition capable of forming a cured coating film which is excellent in performances such as throwing power, electrodeposition coating aptitude for rust preventive steel plate, and corrosion resistance.
Cationic electrodeposition paint composition has been used mainly as an electrodeposition paint for a wide range of uses such as undercoating of a car body. Products having various properties have been developed up to now. For example, there has been proposed a cationic electrodeposition paint composition excellent in corrosion resistance and in electrodeposition coating aptitude for rust preventive steel plate and further in adhesion, which contains, as a base resin, an epoxy resin which contains amino group and/or quaternary ammonium group as water-soluble group, and which has been internally plasticized with a plasticizer such as polyamide, polyester, polyether etc. In such a cationic electrodeposition paint composition, there are compounded, as anticorrosive pigment, lead compounds or chromium compounds, for example, lead chromate, basic lead silicate, strontium chromate, etc. Recently, however, the use of such harmful compounds as lead compounds or chromium compounds is restricted in terms of pollution problems, and the development of a cationic paint composition, excellent in corrosion resistance and containing neither lead compounds nor chromium compounds, has been strongly desired.
Since an epoxy resin which is internally plasticized with a plasticizer tends to deteriorate the corrosion resistance of a coating film, it may be considered to improve the corrosion resistance by using, as base resin, an epoxy resin containing no plasticizing modifier. There is, however, a problem that a paint composition using a non-plasticized epoxy resin has a lower electrocoating aptitude for rust preventive steel plate.
Moreover, it has been proposed to compound in an epoxy resin a plasticizer which does not deteriorate the corrosion resistance of a coating film, for example, polyol resin such as polyester polyol polyether polyol polyurethane polyol, acrylpolyol etc.; polyolefin such as polybutadiene, polyethylene, etc. There are problems, however, that these materials are not compatible enough with epoxy resin, and are not only poorly effective to improve the electrocoating aptitude for rust preventive steel plate but also deteriorate, if compounded much, the corrosion resistance of a coating film.
The inventors of the present invention have made assiduous study with a view to resolving the above-mentioned problems, and, as a result, have found out that, when a certain kind of specific amino group-containing epoxy resin is compounded, there is obtained a cationic electrodeposition paint composition which is excellent in all of throwing power, electrocoating aptitude for rust preventive steel plate and corrosion resistance in a well-balanced manner, and, thus, have completed the present invention.
Thus, according to the present invention, there is provided a cationic paint composition containing, as resin component, an amino group-containing epoxy resin obtained by the reaction of:
(A) an epoxy resin with an epoxy equivalent of 300-2,500, with
(B) a hydroxyl group-containing carboxylic acid which is obtained by making hydroxy monocarboxylic acid (b1) react with caprolactone (b2), and
(C) an amino group-containing compound.
In the following, the cationic paint composition provided by the present invention is described in more detail.
(A) Epoxy Resin
Epoxy resin (A) to be the main skeleton of the amino group-containing epoxy resin according to the present invention has suitably an epoxy equivalent in the range of 300-2,500, preferably 350-2,000, and more desirably 400-1,500, and a number-average molecular weight of generally at least 500, preferably in the range of 500-5,000, and more desirably 800-3,000. If the epoxy equivalent of the epoxy resin is less than 300, the corrosion resistance and throwing power of the formed cationic paint composition becomes poor. If, on the other hand, it is more than 2,500, electrocoating aptitude for the rust preventive steel plate (zinc-plated steel plate) is deteriorated.
As such an epoxy resin (A), a product obtained by a reaction of a polyphenol compound with an epihalohydrin, for example, epichlorohydrin, is preferable from a viewpoint of corrosion resistance etc. of coating film.
As a polyphenol compound usable for the formation of said polyepoxide compound, there can be mentioned, for example, bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxy-benzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-iso-butane, bis(4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4-dihydroxydiphenylsulfone, phenol novolac, cresol novolac, etc.
As an epoxy resin obtained by the reaction of polyphenol compound and epichlorohydrin, a product derived from bisphenol A which is illustrated by the following formula: 
wherein n=0-8
is preferable in particular.
As such an epoxy resin available on the market, there can be mentioned, for example, products sold by Japan Epoxy Resin Co., Ltd., under the trade name of Epicote 828EL, 1002, 1004 and 1007.
(B) Hydroxyl Group-Containing Carboxylic Acid
Hydroxyl group-containing carboxylic acid which is to be made to react with the above-mentioned epoxy resin (A) in accordance with the present invention is useful for the internal plasticization of said epoxy resin, and is obtained by making hydroxy monocarboxylic acid (b1) react with caprolactone (b2).
Hydroxy monocarboxylic acid (b1) is a compound which contains, in a molecule, at least one, preferably one or two, hydroxyl groups and a carboxylic acid. Concrete examples include glycolic acid, hydroxy pivalic acid, dimethylol propionic acid, dimethylol butanoic acid, lactic acid, glyceric acid, etc., among which glycolic acid, hydroxy pivalic acid, dimethylol propionic acid and dimethylol butanoic acid are in particular preferable.
As caprolactone (b2) which is to be made to react with the above-mentioned hydroxy monocarboxylic acid (b1), there can be mentioned xcex3-caprolactone, xcex5-caprolactone and xcex4-caprolactone, among which xcex5-caprolactone is especially suitable.
The above-mentioned reaction between hydroxy monocarboxylic acid (b1) and caprolactone (b2) may be carried out by any known method. Concretely, for instance, said reaction can be conducted by heating hydroxy monocarboxylic acid (b1) and caprolactone (b2) at a temperature of about 100 to about 250xc2x0 C. for about one to about 15 hours in the presence of a catalyst such as titanium compound like tetrabutoxy titanium or tetrapopoxy titanium; organotin compound like tin octylate, dibutyl tin oxide or dibutyl tin laurate; and metal compound like stannous chloride.
The above-mentioned catalyst may be used in an amount of 0.5 to 1,000 ppm on the basis of the total amount of hydroxy monocarboxylic acid (b1) and caprolactone (b2). Caprolactone (b2) may be used generally in a range of 1.5 to 15 moles, preferably 1.5 to 13 moles, more desirably 1.7 to 12 moles, per equivalent of hydroxyl group (i.e., per one hydroxyl group) of hydroxy monocarboxylic acid (b1).
(C) Amino Group-Containing Compound
An amino group-containing compound (C) to be made to react with the aforementioned epoxy resin (A) in the present invention is a component to give the cationicity to cationize said epoxy resin by introducing amino group to epoxy resin substrate. There is used a compound containing at least one active hydrogen which reacts with an epoxy group.
As an amino group-containing compound used for such a purpose, there can be mentioned, for example, mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, diisopropylamine, trilsopropylamine, monobutylamine, dibutylamine, etc.; alkanolamines such as monoethanolamine, diethanolamine, mono(2-hydroxypropyl)amine, di(2-hydroxypropyl)amine, tri(2-hydroxypropyl)amine, monomethylaminoethanol monoethyl-aminoethanol, etc.; alkylenepolyamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, tetraethylenepentamine, pentaethylenehexamine, diethylamino-propylamine, diethylenetriamine, triethylenetetramine, etc., and ketiminized products of these polyamines; alkyleneimines such as ethyleneimine, propyleneimine, etc.; cyclic amines such as piperazine, morpholine, pyrazine, etc.
Amino Group-Containing Epoxy Resin
Amino group-containing epoxy resin which is used as vehicle in the paint composition of the present invention can be prepared by a reaction of the aforementioned epoxy resin (A) with hydroxyl group-containing carboxylic acid (B) and amino group-containing compound (C) by a known process. Reactions of hydroxyl group-containing carboxylic acid (B) and amino group-containing compound (C) to the epoxy resin (A) may be conducted in an optional order. Generally, however, it is preferable to make hydroxyl group-containing carboxylic acid (B) and amino group-containing compound (C) react to the epoxy resin (A) at the same time. The reaction of hydroxyl group-containing carboxylic acid (B) with the epoxy resin (A) is an addition reaction of carboxylic group of hydroxyl group-containing carboxylic acid (B) to epoxy group of the epoxy resin (A). The addition reaction of hydroxyl group-containing carboxylic acid (B) and amino group-containing compound (C) to epoxy resin (A) may usually be conducted in a suitable solvent at a temperature of about 80 to about 200xc2x0 C., preferably about 85 to about 150xc2x0 C., until the acid value of reaction mixture becomes at most 2 mgKOH/g. As the above-mentioned solvent, there can be mentioned, for example, hydrocarbons such as toluene, xylene, cyclohexane, n-hexane, etc.; esters such as methyl acetate, ethyl acetate, butyl acetate, etc.; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, etc.; amides such as dimethylformamide, dimethylacetamide, etc.; alcohols such as methanol, ethanol, n-propanol, isopropanol, etc.; and their mixtures.
Ratio of usage of each reaction component in the above-mentioned reaction is not strictly limited but can be varied suitably according to the application of the paint composition etc. The following ranges, however, based upon the total solid content weight of the three components, epoxy resin (A), hydroxyl group-containing carboxylic acid (B) and amino group-containing compound (C), are appropriate.
Epoxy Resin (A):
Generally 55-85% by weight, preferably 55-80% by weight;
Hydroxyl Group-Containing Carboxylic Acid (B):
Generally 5-30% by weight, preferably 5-25% by weight;
Amino Group-Containing Compound (C):
Generally 5-25% by weight, preferably 6-22% by weight.
Cationic Paint Composition
The cationic paint composition provided by the present invention contains as vehicle, an amino group-containing epoxy resin which is prepared in the afore-mentioned manner, and is preferably used in water-borne paint, particularly electrodeposition paint.
The amino group-containing epoxy resin according to the present invention gives a thermosetting cationic paint composition when combined with a crosslinking agent, for example, blocked polyisocyanate, melamine resin, etc., particularly blocked polyisocyanate crosslinking agent.
The above-mentioned blocked polyisocyanate crosslinking agent is an addition reaction product of a polyisocyanate compound and an isocyanate-blocking agent in an approximately stoichiometric amount. As a polyisocyanate compound used in this case, there can be mentioned, for example, aromatic, aliphatic or alicyclic polyisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis(isocyanatomethyl)-cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, isophoron diisocyanate, etc., and compounds containing terminal isocyanate obtained by a reaction of an excess amount of these isocyanate compounds with a low molecular active hydrogen-containing compound such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, castor oil, etc. These can be used either singly or in combination of two kinds or more. Among them, in particular aromatic diisocyanate, above all crude MDI, is preferable.
Crude MDI is a mixture of diphenylmethane-4,4xe2x80x2-diisocyanate, diphenylmethane-2,4xe2x80x2-diisocyanate and polymethylene polyphenyl polyisocyanate as main components. There can be mentioned, as commercial products, Cosmonate M-50, M-200, M-100, M-300, etc. (made by Mitsui Chemicals, Inc.); Sumidur 44V10, 44V20, 44V40, etc. (made by Sumika Bayer Urethane Co., Ltd.); Lupranate M-12, M-12S, M-20, M20S, etc. (made by BASF, Germany); Mondur MR (LIGHT) etc. (made by Bayer), etc.
On the other hand, the afore-mentioned isocyanate blocking agent is a substance to be added to, and to block, an isocyanate group of a polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is desirably stable at normal temperature, and capable of reproducing a free isocyanate group, dissociating the blocking agent, at the time of being heated to a baking temperature (usually about 100-about 200xc2x0 C.) of the coating film. As a blocking agent meeting such requirements, there can be mentioned, for example, lactam type compounds such as xcex5-caprolactam, xcex3-butyrolatam, etc.; oxime type compounds such as methyl ethyl ketoxime, cyclohexanone oxime, etc.; phenol type compounds such as phenol, p-t-butylphenol, cresol, etc.; aliphatic alcohols such as n-butanol, 2-ethylhexanol, etc.; aromatic alkyl alcohols such as phenylcarbinol, methyl-phenylcarbinol, etc.; ether alcohol type compounds such as ethylene glycol monobutyl ether, etc.
Compounding ratio of an amino group-containing epoxy resin and a blocked polyisocyanate crosslinking agent can generally be in the range of 50-80% by weight, preferably 55-75% by weight, and more desirably 55-70% by weight of the amino group-containing epoxy resin, and generally 50-20% by weight, preferably 45-25% by weight, and more desirably 45-30% by weight of the blocked polyisocyanate crosslinking agent, based upon the total solid content weight of both components.
The cationic paint composition of the present invention containing the above-mentioned amino group-containing epoxy resin and a blocked polyisocyanate crosslinking agent can be prepared, for example, by sufficiently mixing the amino group-containing epoxy resin and the blocked polyisocyanate crosslinking agent, and then by water-solubilization or water-dispersing of said epoxy resin through neutralization with a water-soluble organic carboxylic acid usually in an aqueous medium. As an organic carboxylic acid for neutralization, particularly acetic acid, formic acid or their mixture is preferable. By using these acids, finishing property, throwing power and low temperature curability of the formed paint composition and stability of the paint are improved.
In the paint composition of the present invention, a bismuth compound can be included as anticorrosive agent. There is no restriction in the kind of bismuth compound to be compounded. Examples are inorganic bismuth compounds such as bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate, etc., among which, particularly bismuth hydroxide is preferable.
Moreover, it is possible to use, as a bismuth compound, an organic bismuth salt which is prepared by a reaction of a bismuth compound as mentioned above and two or more kinds of organic acids, at least one of which is an aliphatic hydroxycarboxylic acid. As an organic acid usable for the preparation of said organic bismuth salt, there can be mentioned, for example, glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethy-lolbutyric acid, dimethylolvaleric acid, tartaric acid, malic acid, hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, benzoic acid, citric acid, etc.
The above-mentioned inorganic bismuth compounds and organic bismuth salts can each be used, either singly or in combination of two kinds or more.
Content of these bismuth compounds in the paint composition of the present invention is not strictly limited but can be varied in a wide range according to the performances required of the paint etc. Usually, however, less than 10% by weight, preferably the range of 0.05-5% by weight, based upon the resin solid content in the paint composition of the present invention, is appropriate.
The cationic paint composition of the present invention can further contain, optionally, a tin compound as a curing catalyst. As said tin compound, there can be mentioned, for example, organotin compounds such as dibutyltin oxide, dioctyltin oxide, etc.; aliphatic or aromatic carboxylates of dialkyltin such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoateoxy, dioctyltin dibenzoate, dibutyltin dibenzoate, etc., among which dialkyltin aromatic carboxylates etc. are preferable from the viewpoint of low temperature curability.
The content of such a tin compound in the paint composition of the present invention is not strictly prescribed but can be varied in a wide range according to the performances required of the paint etc. The tin content, however, is preferably in the range of usually 0.01-8 parts by weight, preferably 0.05-5 parts by weight per 100 parts by weight of the resin solid content in the paint.
In the cationic paint composition of the present invention, there can be further compounded, if necessary, additives for paint such as color pigment, extender pigment, anticorrosive pigment, organic solvent, pigment dispersing agent, surface adjustment agent, etc.
The cationic paint composition of the present invention is applied onto the surface of a desired substrate by cationic electrodeposition coating. The electrodeposition coating can be conducted generally in an electrodeposition bath comprising the paint composition of the present invention which has been diluted with deionized water etc. so that the solid content concentration may become about 5-about 40% by weight, preferably 15-25% by weight, and pH of which has been adjusted in the range of 5.5-9 under the condition of the bath temperature usually set at about 15-about 35xc2x0 C. and the load voltage at 100-450V.
The film thickness of the electrodeposition coating film formed by using the paint composition of the present invention is not particularly limited, but is preferably generally in the range of 10-45 xcexcm, particularly 15-30 xcexcm, based upon a cured coating film. The baking temperature of the coating film is suitably generally in the range of about 120-about 200xc2x0 C., preferably about 140-about 180xc2x0 C., at the surface of the substrate. The baking time can be about 5-60 minutes, preferably about 10-30 minutes.
The cationic paint composition of the present invention is used preferably as cationic electrodeposition paint. Besides it can also be used as solvent type paint, as an anticorrosive primer for a steel plate to be coated by means of electrodeposition coating, roller coating, etc.
Furthermore, the paint composition of the present invention is usable as two-liquid type, room temperature-drying paint with polyisocyanate compound or melamine resin as crosslinking agent or adhesive.
The cationic paint composition of the present invention forms a cured coating film excellent in corrosion resistance, electrocoating aptitude for rust preventive steel plate and adhesion to the substrate, and is useful, for example, as undercoat paint for car body, car parts, and in the field of construction and architecture, etc.
Especially, of a cationic electrodeposition paint, a throwing power is required as a rust preventive countermeasure for baggy parts of a car body (locker, side-sill, pillar). Higher throwing power is being required because of more and more complicated body structure which has been caused by reinforcement member provided in locker part and side-sill too meet the recent demand for better safety.
The cationic paint composition of the present invention has a high throwing power, and can form an electrodeposition coating film excellent in corrosion resistance with excellent electrodeposition coating aptitude even for a car body with complicated structure.
In the following, the present invention is described more specifically by working examples. The present invention shall however, not be restricted to these examples in any way. xe2x80x9cPartxe2x80x9d and xe2x80x9c%xe2x80x9d means xe2x80x9cpart by weightxe2x80x9d and xe2x80x9c% by weightxe2x80x9d, respectively.